Food allergy may induce a harmful immune response such as dermatitis, asthma, or anaphylactic shock, and has a risk leading to a fatal accident. In fact, it has been reported that about 150 people die from food allergy per year in the United States. In view of such a situation, many techniques for detecting an allergen in food have been proposed.
Currently, immunoassay using an antibody is generally used as a method for detecting an allergen. For example, Patent Literature 1 discloses a method for detecting a buckwheat allergen by ELISA or immunochromatography.
Meanwhile, a method for detecting an allergen in a sample using a mass spectrometer has been proposed. Patent Literature 2 discloses a method for detecting an allergen by liquid chromatography tandem mass spectrometry (LC-MS/MS).
Patent Literature 3 discloses a method for quantifying a specific protein contained in a sample by performing mass spectrometry by mixing a stable isotope-labeled protein with a sample, quantifying a plurality of peptide fragments based on a signal area ratio and a signal intensity ratio between a target protein-derived peptide fragment and a stable isotope-labeled protein-derived peptide fragment, and calculating an average value of the quantitative values of the peptide fragments.
By the way, a proteome is a collection of proteins existing in a biological system such as a cell, a tissue, or an organism. Comparing proteomes in a plurality of systems makes it possible to comprehensively understand a life phenomenon. A method for approaching a life phenomenon by comprehensively analyzing a proteome is referred to as proteomics.
In recent years, with development of mass spectrometry, it has become possible to accurately measure the mass of a small amount of protein fragments, and a method combining mass spectrometry with proteomics has been developed. Specifically, it has become possible to separate a protein contained in a proteome by electrophoresis, chromatography, or the like, to specify a protein having a difference in expression in a plurality of biological systems, to fragment the protein and measure the mass of the fragmented protein, and to identify the protein by comparing the obtained data with amino acid sequence data of a protein presumed from genome analysis.
As described above, with development of mass spectrometry, a proteomics technique has advanced dramatically, and has been actively performed not only in a basic research field of life science but also in a field of medical science searching for a causal protein of a human disease such as cancer (for example, Patent Literature 4).
After a specific protein is identified by mass spectrometry, it is required to detect the protein in a proteome for functional analysis of the protein. Therefore, a method for qualitatively or quantitatively detecting a specific protein in a proteome has been desired.
Under such a situation, as a method for quantifying a specific protein in a proteome, a method for performing relative quantification based on a peak intensity ratio in mass spectrometry while a stable isotope is used and one sample is used as an internal standard, has been proposed (Non-Patent Literature 1).
In addition, an ICAT method using chemical modification on a cysteine residue as a label instead of an isotope has been proposed (Non-Patent Literature 1).
By the way, immunoassay for performing an antigen-antibody reaction in the presence of an ionic surfactant is known (for example, Patent Literatures 5 and 6). In this method, a protein denatured by an ionic surfactant is detected.